This invention relates generally to brush seals and more particularly to brush seals for use in gas turbine engines.
A gas turbine engine operates according to well known principles wherein an incoming stream of atmospheric air flows through the engine along an axially extending flow path. At least a portion of the incoming air is compressed in a compressor section of the engine and then mixed with fuel and burned in a combustor section to produce a high energy, high temperature exhaust gas stream. The hot gas stream exits the combustor and subsequently passes through a turbine section that extracts energy from the exhaust gas stream to power the compressor and provide useful work such as powering an aircraft in flight.
Uncontrolled leakage of gasesxe2x80x94such as atmospheric air, exhaust gases, or otherxe2x80x94within the engine contributes to a reduced engine efficiency. Seals are used to control this energy loss by interposing them in a leakage path to reduce the volume or mass of gas passing from one part of the engine to another. Labyrinth seals have been commonly used in gas turbine engines for sealing between relatively movable components. However, the use of brush seals as a substitute for labyrinth seals is also known.
A conventional brush seal typically includes a bristle pack having a plurality of bristles disposed between a pair of annular plates. The bristles usually are disposed at about a forty five degree angle to a radius drawn from the engine centerline. A brush seal is typically attached along its outer radial edge to a stationary engine part with the radially inner, free ends of the bristles disposed in a sealing engagement with a sealing surface on a rotating engine part. Brush seals are not intended to function so as to completely seal one engine section from another, but rather rely upon the tortuous flow path created between the bristles to reduce gas flow therethrough and to control the pressure drop between the engine sections.
The bristles in the bristle pact are somewhat flexible and are thus able to bend during an engine transient and still retain their sealing ability after the transient has passed. Examples of such transients include differential thermal growth between the stationary and rotating engine parts and relative lateral motion between the stationary and rotating engine parts due to engine vibrations and/or eccentric shaft rotation. The sealing efficiency of a brush seal over time is affected by the wear on the bristle ends contacting the sealing surface on the rotating engine part, as well as the overall contact of the bristle ends with the sealing surface. However, in some instances, the relative lateral motion between the engine parts can be of a magnitude large enough to cause significant bristle flexure, which leads to premature and excessive wear on the bristles. Premature bristle wear will require replacement of the seal or bristle pack earlier than otherwise would be necessary, thereby increasing engine operating costs.
It would be desirable to increase the lifetime and sealing efficiency of brush seals by reducing premature and excessive bristle wear due to significant engine alignment offsets.
The above-mentioned need is met by the present invention, which provides a brush seal having a holder and a carrier moveably suspended from the holder by a plurality of flexible support wires. A plurality of bristles is secured to the carrier. Preferably, the holder is attached to a stationary member, and the bristles sealingly engage a rotating member.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.